Dose and dose rate effectiveness to determine the risk of low dose radiation to human

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1.0.5 and 1.7 Gy of ^<60>Co-gamma radiation was given to 6 weeks old C3H/HeJ and C57BL/6J mice 4 times at 7 days interval at different dose rates from 0.0002 to 0.57 Gy/min, and Dose and Dose Rate Effectiveness Factor (DDREF) was calculated for the risk estimation.(1) There were apparent dose rate effects in leukemia induction. DDREF was 20-40. Delayed increase of solid tumors was also observed by the lowere dose rates.(2) There was a slight reduction of solid tumors by lower dose rate in C57BL/6J mice, but nothing in C3H/HeJ mice (DDREF*1.0). However, dose rate effects were detected in the lung, breast, and pituitary tumors (DDREF*2.3).2. Fetal deaths, malformations somatic mutation and tumors were induced in PTHTF mice after in utero doses of X-rays, ^<60>Co-rays, and ^<252>Cf neutron. About 1/3 reduction of these defects was observed by lower dose rate. RBE of ^<252>Cf was 6-9 for mutation and cancer.3. PLDR and dose rate effects were absent or very small in double strand breaks repair deficient SCID cells, white it was obvious in wild type culture cells, indicating that dose rate effects were caused by double strand breaks repair in the most parts.4. Measurement of the expression level of WT 1 gene is carried out for the liquidators with hematological abnormality after Chernobyl catastrophe, because it is extremely sensitive to detect leukemia in human.